Hi Wally, this is a very good question.
Does the design only contain photos? If so, then no, there's no difference between a jpeg and a pdf. In fact, your photos will simply be jpegs inside the pdf.
But if there are other elements - eg text or logos - then PDF is crucial.
https://www.damiensymonds.net/2010/05/making-pdfs-from-photoshop.html